This invention is particularly suited for in situ applications of liquid chemicals mixed and dispensed as a spray or a foam and more specifically, to in situ application of polyurethane foam or froth. In situ applications for polyurethane foam have continued to increase in recent years extending the application of polyurethane foam beyond its traditional uses in the packaging, insulation and molding fields. For example, polyurethane foam is being used with increasing frequency as a sealant in the building trades for sealing spaces between windows and door frames and the like and as an adhesive for gluing flooring, roof tiles, and the like.
Polyurethane foam for in situ applications is typically supplied as a “one-component” froth foam or a “two-component” froth foam in portable containers hand carried and dispensed by the operator through either a valve or a gun. However, the chemical reactions producing the polyurethane froth foam in a “one-component” polyurethane foam is different at time of application than the chemical reactions producing a polyurethane froth foam in a “two-component” polyurethane foam. Because the reactions proceed differently, the dispensing of the chemicals for a two-component polyurethane foam involves different and additional concepts and concerns than that present in the dispensing apparatus for a “one-component” polyurethane froth foam.
A “one-component” foam generally means that both the resin and the isocyanate used in the foam formulation are supplied in a single pressurized container and dispensed from the container through a valve or a gun attached to the container. When the chemicals leave the valve, a reaction with moisture in the air produces a polyurethane froth or foam. Thus, the design concerns related to an apparatus for dispensing one-component polyurethane foam essentially concerns the operating characteristics of how the one-component polyurethane foam is throttled or metered from the pressurized container. Reference, for example, can be had to U.S. Pat. No. 5,887,756 to Brown, issued Mar. 30, 1999 and U.S. Pat. No. 5,645,199 to Schnitzler, issued Jul. 8, 1997. While one-component guns can variably meter the polyurethane froth, they are typically used in caulk/glue applications where an adhesive or caulk bead is determined by the nozzle configuration. Post drip is a major concern in such applications as well as the dispensing gun not clogging because of reaction of the one component formulation with air (moisture) within the gun. To address or at least partially address such problems, a needle valve seat is typically applied as close to the dispensing point by a metering rod arrangement which can be pulled back for cleaning. While metering can occur at the needle valve seat, the seat is primarily for shut-off to prevent post drip, and depending on gun dimensioning, metering may principally occur at the gun opening.
In contrast, a “two-component” froth foam means that one principal foam component is supplied in one pressurized container, typically the “A” container (i.e., polymeric isocyanate, fluorocarbons, etc.) while the other principal foam component is supplied in a second pressurized container, typically the “B” container (i.e., polyols, catalysts, flame retardants, fluorocarbons, etc.) Examples of two-component dispensing guns in commercial use today may be found in assignee's U.S. Pat. No. 5,429,308, to Brown, issued Jul. 4, 1995 and U.S. Pat. No. 5,242,115 to Brown, issued Sep. 7, 1993 and in the parent application incorporated by reference herein. Additional commercial applications include U.S. Pat. No. 5,462,204 to Finn, issued Oct. 31, 1995; U.S. Pat. No. 5,129,581 to Braun et al., issued Jul. 14, 1992; and, U.S. Pat. No. 4,925,107 to Brown, issued May 15, 1990. These guns are improvements over early two-component dispensing gun designs such as shown in U.S. Pat. No. 2,890,836 to Gusmer et al., issued Jun. 16, 1959; U.S. Pat. No. 3,559,890 to Brooks, issued Feb. 2, 1971; and, U.S. Pat. No. 3,784,110 to Brooks, issued Jan. 8, 1974.
In a two-component polyurethane foam, the “A” and “B” components form the foam or froth when they are mixed in the gun nozzle. Of course, chemical reactions with moisture in the air will also occur with a two-component polyurethane foam after dispensing, but the principal reaction forming the polyurethane foam occurs when the “A” and “B” components are mixed or contact one another in the dispensing gun nozzle. The dispensing apparatus for a two-component polyurethane foam application has to thus address not only the metering design concerns present in a one-component dispensing apparatus, but also the mixing requirements of a two-component polyurethane foam.
Further, a “frothing” characteristic of the foam (foam assumes consistency resembling shaving cream) is enhanced by the fluorocarbon (or similar) component, which is present in the “A” and “B” components. This fluorocarbon component (HFC or HCFC) is a compressed gas which exits in its liquid state under pressure and changes to it gaseous state when the liquid is dispensed into a lower pressure ambient environment, such as when the liquid components exit the gun and enter the nozzle of the gun to which this invention relates.
While polyurethane foam is well known, the formulation varies considerably depending on application. In particular, while the polyols and isocyanates are typically kept separate in the “B” and “A” containers, other chemicals in the formulation may be placed in either container (but generally the chemical additives are placed in the “B” side) with the result that the weight or viscosity of the liquids in each container varies as well as the ratios at which the “A” and “B” components are to be mixed. In the nozzle for the dispensing gun applications which relate to this invention, the “A” and “B” formulations are such that the mixing ratios are generally kept equal so that the “A” and “B” containers are the same size. However, the weight, more importantly the viscosity, of the liquids in the containers invariably vary from one another. To adjust for viscosity variation between “A” and “B” chemical formulations, the “A” and “B” containers are charged with differing concentrations of HFC or HCFC component typically with an inert gas at different or similar pressures to achieve equal flow rates. The metering valves in a two-component gun, therefore, have to meter different liquids at their separate pressures at a precise ratio under varying flow rates. For this reason (among others), some dispensing guns have a design where each metering rod/valve is separately adjustable against a separate spring to compensate not only for ratio variations in different formulations but also viscosity variations between the components. The typical two-component dispensing gun in use today can be viewed as two separate one-component dispensing guns in a common housing discharging their components into a mixing chamber or nozzle.
Besides the ratio control which distinguishes two-component dispensing guns from one-component dispensing guns, a concern which affects all two-component gun designs (not present in one-component dispensing guns) is known in the trade as “cross-over”. Generally, “cross-over” means that one of the components of the foam (“A” or “B”) has crossed over into the dispensing mechanism in the dispensing gun for the other component (“B” or “A”). Cross-over may occur, for example, when the pressure variation between the “A” and “B” cylinders becomes significant. Variation can become significant when the foam formulation initially calls for the “A” and “B” containers to be at high differential charge pressures and the containers have discharged a majority of their components. (The containers are accumulators which inherently vary the pressure as the contents of the container are used.) Another example of a cause of cross-over is nozzle clogging or obstruction (discussed further below).
Related to cross-over and affecting the operation of a two-component gun is the design of the nozzle. The nozzle is a throw away item detachably mounted to the gun nose. Nozzle design is important for cross-over and metering considerations in that the nozzle directs the “A” and “B” components to a static mixer in the gun. One gun described in U.S. Pat. No. 5,462,204 completely divides the nozzle into two passages by a wall extending from the nozzle nose (gun face) to the mixer. The wall lessens but does not eliminate the risk of cross-over since the higher pressurized component must travel into the mixer and back to the lower pressure metering valve before cross-over can occur. However, the nozzle design illustrated in the '204 patent may be limited because of the wall and nozzle inlet chamber tending to create turbulence for applications requiring very high flow rates.
A still further characteristic distinguishing two-component from one-component gun designs resides in the clogging tendencies of two-component guns. Because the foam foaming reaction commences when the “A” and “B” components contact one another, it is clear that, once the gun is used, the static mixer will clog with polyurethane foam or froth formed within the mixer. This is why the nozzles, which contain the static mixer, are designed as throw away items. In practice, the foam does not instantaneously form within the nozzle upon cessation of metering to the point where the nozzles have to be discarded. Some time must elapse. This is a function of the formulation itself, the design of the static mixer and, all things being equal, the design of the nozzle.
The spray pattern produced by the nozzle is important. Typically, the nozzle tip is simply the circular end of a tube producing a cone fan pattern. However, reference can be had to assignee's U.S. Pat. No. 5,429,308 which discusses a flared or funnel nozzle for producing a fan shaped spray and to U.S. Pat. No. 5,129,581 which discloses a “V” notch in the nozzle tip and has been well received within the industry. What is required is a nozzle that produces a consistent fan spray pattern, preferably a well defined pattern, which can be maintained at full throttle flow of the components and at throttled or “fine” flow of the components. In addition, the consistency of the flow pattern has to be maintained notwithstanding the fact that the pressure of the liquid components flowing through the gun drops as the pressurized containers (for portable gun application) dispel their foam producing components.
Even when a well defined spray pattern is produced under all operating conditions of the nozzle, other considerations are of major concern. If at all possible, nozzle drip has to be avoided. Nozzle drip conventionally means that a foam buildup occurs at the nozzle tip resulting in dripping during gun operation.
Another important requirement for a “good” nozzle is the time it takes for the nozzle to “clog” after the gun has been shut off. The nozzle is a throw away component and inevitably the foam components will react and produce foam in the nozzle, clogging the nozzle. In many applications, the gun is used intermittently. For example, a mold may be filled or a part sprayed and measurements initially taken after which additional coating may have to be sprayed. Generally speaking, a “plug” is formed in the nozzle when the gun stops spraying. The “plug” grows over time. If the gun is activated after spraying and the “plug” has not grown significantly, the plug” will be discharged from the gun on reactivation and the gun will continue to function. For polyurethane foam applications, nozzles have been known to clog within thirty seconds and some gun/nozzle applications can be idled for up to 4½ to 5 minutes without clogging. In all cases, nozzle/gun design, formulation and environmental conditions are contributing factors.
The dispensing guns cited when equipped with the inventive nozzle are additionally characterized and distinguished from other types of multi-component dispensing guns in that they are “airless” and do not contain provisions for cleaning the gun. That is, a number of dispensing or metering guns or apparatus, particularly those used in high volume foam applications, are equipped or provided with a means or mechanism to introduce air or a solvent for cleaning or clearing the passages in the gun. The use of the term “airless” as used in this patent and the claims hereof means that the dispensing apparatus is not provided with an external, cleaning or purging mechanism.
While the two-component dispensing guns discussed above function in a commercially acceptable manner, it is becoming increasingly clear as the number of in situ applications for polyurethane foam increase, that the range or the ability of the dispensing gun to function for all such applications has to be improved. As a general example, the dispensing gun design has to be able to throttle or meter a fine bead of polyurethane froth in a sealant application where the kit is sold to seal spaces around window frames, door frames, and the like in the building trade. In contrast, where the kit is sold to form insulation, an ability to meter or flow a high volume flow of chemicals is required. Still yet, in an adhesive application, liquid spray patterns of various widths and thickness are required. Additionally, there are yet other desirable configurations for the filling of molds. While the “A” and “B” components for each of these applications are specially formulated and differ from one another, one dispensing gun for all such applications involving different formulations of the chemicals is needed, and the nozzle applied to the gun must be able to spray the components in a consistent manner over the wide operating range requirements of the gun.